1. Field of the Invention
The present invention relates to a droplet ejection apparatus, such as an inkjet printer, capable of ejecting droplets of a liquid such as ink, and more particular to an operation of the droplet ejection apparatus for preventing a poor droplet ejection performance due to drying of the liquid contained inside of a nozzle.
2. Discussion of Related Art
There has conventionally been known an inkjet printer including a recording head which is mounted on a carriage and which has a plurality of nozzles provided on a lower surface thereof. In the conventional inkjet printer, while the recording head is reciprocated in a recording area, a recording operation in which droplets of ink are ejected onto a recording medium is performed so as to record an image thereon. In the recording operation, drive pulses are inputted into a piezoelectric actuator such that volumes of pressure chambers which are filled with the cink are changed. Thus, the ink droplets are ejected from the plurality of nozzles of the recording head toward an upper surface of the recording medium.
In the conventional inkjet printer which employs the recording head having the plurality of nozzles through which the ink droplets are ejected, a solvent of the ink, e.g., water, is gradually dried up in the nozzles due to an intermission of the recording operation or few opportunities of ink-droplet ejections, and thus, the ink becomes thickened in the nozzles. Consequently, the ink droplets which are ejected from the nozzles tend to be decreased in size, or an ink-droplet ejection performance of the recording head tends to be deteriorated. This state causes a deterioration in a recording performance of the recording head.
In order to avoid the above-described deterioration in the recording performance, a preparatory ink-droplet ejection, i.e., so-called “a flushing operation”, is performed before a recording process or in the middle of a recording process. In the flushing operation, the recording head is moved regularly or forcibly to a flushing position where a droplet receiver is disposed such that a lower surface of the recording head faces an upper surface of the droplet receiver. More specifically, the droplet receiver is disposed outside of the recording area, i.e., a non-recording area. After the recording head is moved to the flushing position as a specific position in the non-recording area, the drive pulses are inputted to the actuator such that the ink which remains in the nozzles is forcibly ejected. Thus, the flushing operation is effective to restore the ink-droplet ejection performance of the recording head.
However, the flushing operation may cause an increase in a time required for the recording process and a waste of the ink since the recording operation is inevitably interrupted in order to move the recording head to the flushing position in the non-recording area.
Therefore, as disclosed in JP-A-9-295411 (paragraph [0003] and FIG. 3, in particular) for instance, there has been proposed a droplet ejection apparatus which has first voltage applying means for applying a first voltage that is substantially identical with a head drive voltage generated in the recording operation and second voltage applying means for applying a second voltage that is lower than the first voltage in an absolute value. The disclosed droplet ejection apparatus performs, a plurality of times, a unit restoring operation for restoring the ink-droplet ejection performance of the recording head before the recording operation is performed so as to perform the flushing operation. A procedure of the unit restoring operation includes: (i) an initial step for operating the second voltage applying means a plurality of times at the substantially same period as, or shorter period than, a drive period at which the recording operation is performed; and (ii) a subsequent step for operating the first voltage applying means following the initial step.